The present invention is applicable to the formation of a continuous, perimeter type building foundation comprising a footing cast on earth and a wall cast atop said footing, both constructed of a hardenable plastic material having strength and mechanical characteristics suitable for a building foundation. It is standard, widely accepted practice to construct such foundations of concrete using rigid forms of wood or steel to contain and shape the fluent mixture.
The art of forming building foundations using a plastic concrete mixture is well known and is traditionally accomplished in a multi-step process calling for a number of different skilled craftsmen. A trench of specified width and depth is excavated in the earth to receive a predetermined amount of fluent concrete, which is placed in the trench to a specific depth to form a footing therein of generally a rectangular shape.
Once the footing concrete has hardened, concrete wall forms comprising opposing, parallel, vertical units are constructed on the top surface of said footing using elongate panels, such as sheets of plywood. These forms define the general shape of an elongate foundation wall of predetermined height, width and length on top of the footing. These vertical wall forms are connected in edge to edge fashion and secured to each other, strengthened and braced by additional structural members, and supported by various means on the footing to resist the horizontal forces generated by the fluent concrete mixture.
A second predetermined amount of fluent concrete material is placed between these parallel, elongate panels so as to form a foundation wall therein. Thereafter, the forms are removed from the surface of the hardened concrete foundation wall, and fill material is placed back on top of the footing and next to the walls, completely covering said footing underground and thereby completing the structural foundation construction process.
The wall forms used in this manner are then cleaned, repaired if necessary, oiled (a type of release agent to assist in breaking the chemical bond between the wood and the concrete), removed from the site and transported to the next project, or stored for future use.
The concrete footing and foundation wall thus constructed is generally reinforced with deformed steel rebar, and embedments such as anchor bolts, rebar dowels, metal straps and other attachments are cast into the concrete elements to connect the superstructure above to the foundation system below.
Although several variations of constructing concrete foundations by the above described method exist, the most commonly used procedure is to attach and anchor the foundation wall formwork to the top of the previously placed, hardened concrete footing through the use of metal attachments called form ties.
Generally, form ties are elongate metal straps one or two inches wide, having a short flange extending from each end in a perpendicular fashion to the main portion of the strap, each flange being separated by a predetermined distance from the opposing flange so as to contain and separate the form sidewalls within according to a predetermined wall width. The form ties are commonly attached "flanges up" on the top of the footing so as to restrain, via the upturned flanges, the wall forms between them at a predetermined separation. The form ties are commonly attached "flanges down" to the top of the wall forms, thereby restraining these forms at the top in a similar manner.
Many other types of ties have been used successfully (threaded rods, steel bars and straps, and the like), however, the basic function has remained the same: Hold the opposing, parallel wall forms on the top of the footing together by resisting the outward forces created by the hydrostatic force on the form from the fluent concrete.
Several drawbacks are evident in implementing the above foundation construction process and form support methods, First, the traditional construction process dictates that before the foundation wall can be constructed, the footing below must be placed and allowed to harden. The waiting period required between the construction activities in this process results in additional mobilization of personnel and material, and adds to the length of the construction time. Both of these inherent characteristics of the traditional process significantly increase the overall cost of the foundation system.
Second, the removal, cleaning, oiling, repair, handling, transporting, and storing of the foundation wall forms is a very labor intensive process, requiring significant investments in both time and material. This formwork activity is a major expense item for concrete construction.
Third, the entire traditional process normally requires construction to be accomplished in numerous phases by skilled craftsmen over the span of several days, placing additional economical restraints on the procedure.
Fourth, casting the foundation wall atop the footing after the footing hardens results in a "cold joint," or "weak seam," between the two elements at their intersection. This causes a reduction of structural interaction between the two elements and provides a convenient path for water or moisture to migrate under the structure and floor slabs.
Fifth, a large number of form ties are required to anchor and support the wall forms. Since some of these are left permanently cast in the concrete (typically the bottom ties, occasionally the top ties), a continuing investment in new material is required. Also, the permanently cast bottom tie forms an additional path for moisture penetration through the foundation wall, especially if it becomes corrodded.
Certain prior art in the field of constructing foundations with formed concrete have attempted to address some of the inherent disadvantages of the present technology.
U.S. Pat. No. 4,186,160 discloses a method of forming foundation walls atop the hardened footing that eliminates the use of the bottom form ties by utilizing continuous slots formed in the top of the footing while still plastic within which the plywood wall forms are engaged and supported after the footing concrete hardens. Employing this method of construction does overcome the use of many of the bottom form ties. However, several drawbacks in the present art are not addressed by the method described in the referenced patent:
(1) The footing must still be poured and hardened prior to forming the wall atop; (2) a cold joint is present in the construction; and (3) the plywood wall forms must still be removed, cleaned, oiled, handled and stored for future use.
Certain other prior art, exemplified by U.S. Pat. Nos. 3,762,678 and 3,767,158, among others, disclose improved methods of concrete forming using an ingenious array of clips, supports, braces, attachments and heavily reinforced removable forms. Some of these systems have gained acceptance and use in the construction industry, primarily in the heavy construction sector. This is due mainly to the fact that they can resist very large forces generated by mass concrete construction, and they can be quickly erected for use and dismantled for either storage or reuse on another project. However, their usefulness is diminished in the area of minor, conventional construction, since the fluent concrete pressures are typically very small, the labor intensive form breakdown process is still required, a footing must still be cast and allowed to harden prior to erecting the formwork for the casting of the wall, and these systems normally require significant investments in labor and materials.
Still other species of prior art, exemplified by U.S. Pat. Nos. 4,275,538 and 4,107,889, among others, disclose foundation systems constructed of precast concrete elements utilized in conjunction with site cast units. While these methods do offer certain economies in some situations, their use is somewhat specialized and not readily applicable to common foundation conditions. Also, the majority of the construction contractors who provide material and labor for minor, conventional foundation construction are not equipped to handle precast concrete work.
Therefore, many of the drawbacks listed above in the traditional process of constructing continuous building foundations are not sufficiently addressed by the prior art, nor the traditional methodology. What is needed, and what the present invention provides, is an efficient and economical method of forming the foundation wall atop the footing which simplies the construction process, eliminates inordinate investments in time and material, insures compliance with mandated building codes, and addresses and resolves the above noted drawbacks in the traditional process. While the disclosed process is applicable to all types of construction, it is especially applicable to minor, conventional buildings, such as residential or small commercial construction, where shallow spread footings may be used and no special foundation considerations are required.